1. Field of the Invention
This invention relates to exhaust gas recirculation control valves used in recirculating the exhaust gas from an engine of a motor car.
2. Description of the Prior Art
In general, in the engines of motor cars, as shown in FIG. 1, exhaust gas recirculation control valves 3, which are briefly referred to as the "EGR valves", are provided in a path for communicating an intake system 1 of the engine E with an exhaust system 2 thereof, and the exhaust gas recirculation control valves 3 are adapted to be controlled by a control device 4.
As shown in FIG. 2, the exhaust gas recirculation valves 3 are arranged such that two exhaust gas recirculation control valves 5, 6 are provided in a valve housing 8 successively from an inlet, for receiving the exhaust gas from the engine E, and a valve body 7 is adapted to approach or recede from the control valve 6 provided downwardly in accordance with the action of a diaphragm 9.
However, with the exhaust gas recirculation control valves 3 of the type as described, carbon and the like contained in the exhaust gas tend to be adhesively attached to the interiors of the control valves 5 and 6 constituting throttles. The attachment of carbon and the like thereto results in decreased diameters in paths in the control valves 5 and 6, thus presenting such a disadvantage that the flow rate fluctuates with time.
Heretofore, there have been used control valves 15 and 16 shown in FIGS. 3 and 4, respectively, as the abovedescribed control valves 5 and 6. With these conventional control valves 15 and 16 being not provided at inner wall surfaces of the paths thereof with effective means for gathering carbon and the like, the attachment of carbon and the like on the inner wall surfaces of the paths thereof tends to decrease the diameters of the paths, thus presenting the disadvantage that the flow rate fluctuates with time as described above.